Global%20change%20and%20air%20quality:%20climate,%20background%20ozone,%20nitrogen%20deposition,%20visibility,%20and%20mercury - PowerPoint PPT Presentation

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Global%20change%20and%20air%20quality:%20climate,%20background%20ozone,%20nitrogen%20deposition,%20visibility,%20and%20mercury

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Harvard Atmospheric Chemistry Modeling Group. We work to understand the chemical composition of the atmosphere, the effect of human activity, and the implications for ... – PowerPoint PPT presentation

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Title: Global%20change%20and%20air%20quality:%20climate,%20background%20ozone,%20nitrogen%20deposition,%20visibility,%20and%20mercury


1
Global change and air quality climate,
background ozone, nitrogen deposition,
visibility, and mercury
Daniel J. Jacob
with Eric Leibensperger, Amos Tai, Kevin
Wecht, Lin Zhang, Helen Wang, Rokjin Park, Helen
Amos
2
Harvard Atmospheric Chemistry Modeling Group
We work to understand the chemical composition of
the atmosphere, the effect of human activity, and
the implications for climate change and life on
Earth
Global modeling (GEOS-Chem)
Satellite observations (NASA A-Train)
NASA aircraft missions
3
Air Quality Applied Sciences Team (AQAST)
EARTH SCIENCE SERVING AIR QUALITY MANAGEMENT
NEEDS
19 investigators partnering with AQ managers in a
large number of projects
WORK WITH US! http//acmg.seas.harvard.edu/aqast
4
Effect of climate change on air quality
Expected effect of 21st-century climate change
Observed dependences on meteorological
variables (polluted air)
Ozone PM
Stagnation Temperature Mixing
depth Precipitation Cloud cover Relative
humidity
?

?

?

?
Climate change is expected to degrade ozone air
quality effect on PM uncertain
Jacob and Winner 2009
5
IPCC projection of 21st-century climate change in
N. America
2080-2099 vs. 1980-1999 mean changes for 21
climate models in A1B scenario
Surface temperature
  • Increasing temperature everywhere, largest at
    high latitudes
  • Frequency of heat waves expected to increase
  • Decrease in equator-to-pole contrast expected to
    weaken winds, decrease frequency of mid-latitude
    cyclones and associated cold fronts

IPCC 2007
6
IPCC projection of 21st-century climate change in
N. America
2080-2099 vs. 1980-1999 mean changes for 21
climate models in A1B scenario
Surface temperature
  • Increasing temperature everywhere, largest at
    high latitudes
  • Frequency of heat waves expected to increase
  • Decrease in equator-to-pole contrast expected to
    weaken winds, decrease frequency of mid-latitude
    cyclones and associated cold fronts

IPCC 2007
7
Importance of mid-latitudes cyclones for
ventilating the eastern US
  • Cold fronts associated with cyclones tracking
    across southern Canada are the principal
    ventilation mechanism for the Midwest and East
  • The frequency of these cyclones has decreased in
    past 50 years, likely due to greenhouse warming

Leibensperger et al. 2008
8
Observed trends of ozone pollution and cyclones
in Northeast US
ozone episode days (O3gt80 ppb) and cyclones
tracking across SE Canada in summer 1980-2006
observations
Cyclone track
cyclones ozone episodes
  • Cyclone frequency is predictor of interannual
    pollution variability
  • Observed 1980-2006 decrease in cyclone frequency
    would imply a corresponding degradation of air
    quality if emissions had remained constant
  • Expected of 80 ppb exceedance days for
    Northeast average ozone dropped from 30 in 1980
    to 10 in 2006, but would have dropped to zero in
    absence of cyclone trend

Leibensperger et al. 2008
9
Assessing the effect of 2000-2050 climate
change on ozone air quality in the US
Results from six different coupled
chemistry-climate models
2000-2050 change of 8-h daily max ozone in
summer, keeping anthropogenic emissions constant
ppb
Northeast Midwest California Texas
Southeast
  • Models show consistent projection of ozone
    increase over Northeast
  • Typical mean increase is 1-4 ppb, up to 10 ppb
    for ozone pollution episodes
  • Increase is largest in urban areas with high
    ozone

Weaver et al. 2010
10
Effect of air pollutants on climate change
Radiative forcing is the fundamental metric for
climate science and policy
Solar flux Fin
Terrestrial flux Fout T 4
  • Global radiative equilibrium Fin Fout
  • Perturbation to greenhouse gases or aerosols
    disrupts equilibrium Fin ? Fout
  • ?F Fin - Fout is called the radiative
    forcing
  • Global response of surface temperature is
    proportional to radiative forcing ?Tsurface
    ?F

11
1750-2005 radiative forcing of climate change
  • CO2 forcing is 1.6 0.2 W m-2
  • Methane is the second most important
    anthropogenic greenhouse gas
  • Tropospheric ozone forcing is 0.3-0.7 W m-2
    range reflects uncertainty in natural levels
  • Aerosol forcing could be as large as -2 W m-2
    range reflects uncertainty in aerosol sources,
    optical properties, cloud interactions

IPCC 2007
12
1750-2005 radiative forcing referenced to
emissions
anthropogenic emissions
  • Beneficial impact of methane, BC, CO, NMVOC
    controls
  • Detrimental impact of SO2 and OC controls
  • NOx is climate-neutral within uncertainty

IPCC 2007
13
Methane is win-win for climate and air quality
but only as part of a global strategy
Effect on surface ozone air quality is through
decrease in ozone background and does not depend
on where methane emission is reduced
Reduction in annual MDA8 ozone from 20 global
decrease in anthropogenic methane emissions
West et al., 2006
Global 2005 anthropogenic methane emissions
(EDGAR inventory) US accounts for 10
Source (Tg a-1) US EPA, 2009 Global
Fossil fuel 9.5 80-120
Agriculture 8.2 110-200
Landfills 7.0 40-70
14
Satellite data enable monitoring of US methane
emissions
SCIAMACHY column methane, June-August 2004
Methane observations GEOS-Chem w/EPA
emissions Difference (model-obs)
GEOS-Chem model column methane, 1 July 15
August 2004, using EPA emission estimates
Blue EPA too low Red EPA too high
  • Inventories too low in central US agriculture,
    oil/gas?
  • Inventories too high in New England ??

Kevin Wecht (Harvard)
15
Climate effect from US anthropogenic PM
1950-2050 GEOS-Chem simulation coupled to
NASA/GISS climate model
Radiative forcing from PM
Surface cooling from PM in 1980 (oC)
1950-2050 forcing trend over eastern US
  • Forcing is mostly from sulfate, peaked in
    1970-1990
  • Little leverage to be had from BC control
  • Indirect (cloud) forcing is of similar magnitude
    to direct forcing

Direct
Leibensperger et al., 2012
16
Observed US surface temperature trend
o C
Contiguous US
No warming from 1930 to 1980, sharp warming after
1980
Warming hole observed in eastern US from 1930
to 1990 US PM signature?
GISTEMP 2010
17
1950-2050 surface temperature trend in eastern US
Leibensperger et al. 2012
Observations (GISTEMP) Model (standard)
Model without US anthropogenic PM
  • US anthropogenic PM sources can explain the
    warming hole
  • PM removal has caused accelerated warming in
    eastern US since 1990s

18
Application of GEOS-Chem continental-scale model
simulations to regional/transboundary/intercontine
ntal air quality issues
Continental-scale simulation nested within global
domain
19
Ozone background used in EPA Integrated Science
Assessment
Observations
Standard as described above US background
no US anthro emissions NA background - no
N.American anthro emissions Natural no anthro
emissions worldwide
four GEOS-Chem simulations
2006 MDA8 ozone at Northeast CASTNet sites- with
mean (4th highest) inset
  • Mean NA background over Northeast is 29 ppb
    (spring), 20 ppb (summer)
  • Peak background events of 50 ppb (lightning)
    can lead to total ozone gt 80 ppb

Zhang et al. 2011
20
Model 4th highest MDA8 ozone in 2006
Annual 4th highest ozone
  • Ozone episodes in Northeast usually (not always)
    associated with low background
  • Background will become an important issue as US
    sources decrease and the NAAQS tightens

4th highest NA background value
NA background for annual 4th highest ozone
Zhang et al. 2011
21
Canadian pollution influence on ozone in
Northeast US
Mean Canadian/Mexican pollution influences on
MDA8 ozone (Jun-Aug 2001) as determined by a
GEOS-Chem simulation with those sources shut off
Mean national influence over US is small (3 ppb)
but regional influence can be large
Wang et al. 2009
22
Relevance of Canadian pollution for US air
quality policy
Number of days per year when MDA8 ozone exceeds
75 or 70 ppb and Canadian pollution influence
exceeds 10 ppb
Canadian sources need to be considered in ozone
mitigation plans for Northeast
Wang et al. 2009
23
Decrease of North American NOx emisssions,
2005-2009
as seen with annual mean NO2 columns from the
OMI satellite instrument
2009
2005
Decreases in both the eastern US and eastern
Canada
Shailesh Kharol (Dalhousie)
24
Visibility in US wilderness areas
EPA Regional Haze Rule aims for natural
visibility to be achieved in all US Federal Class
1 areas by 2064 Phase 1 implementation for
2004-2018
GEOS-Chem simulations
Canadian emissions would prevent attainment of
natural visibility in Northeast even with zeroed
US emissions choice of endpoint affects Phase 1
implementation
Park et al. 2006
25
Nitrogen deposition in the US
GEOS-Chem simulation for 2006-2008, reproduces
well NADP data
nominal critical load for ecosystems
  • Nitrogen deposition in the Notheast exceeds
    critical loads
  • Most of that deposition is as nitric acid
    originating from NOx emissions

Zhang et al. 2012
26
Source contributions to nitrogen deposition
as computed from GEOS-Chem sensitivity simulations
US anthropogenic
Foreign anthropogenic
Natural
Nitrogen deposition in Northeast is 10-fold
higher than natural and mainly from domestic
sources
Zhang et al. 2012
27
Mercury (Hg) emissions and deposition in US
Mercury deposition(2008-2009) Circles observed
Background GEOS-Chem
Mercury emissions (EPA)
  • Emission is both as Hg(0) (transported globally)
    and Hg(II) (deposits locally)
  • There is evidence for rapid conversion of Hg(II)
    to Hg(0) in combustion plumes
  • Only 10-20 of mercury deposited in US is of
    direct US anthropogenic origin

Y. Zhang et al. 2012
28
BIOGEOCHEMICAL CYCLING OF MERCURY
very much the same story as carbon
ATMOSPHERE
Hg (gas)
combustion industry mining
deposition re-emission
volcanoes erosion
SOIL
OCEAN
burial
SEDIMENTS
DEEP EARTH
29
Historical inventory of global anthropogenic Hg
emissions
Large legacy contribution from N. American and
European emissions Asian dominance is a recent
phenomenon
Streets et al. , 2012
30
Contribution of old anthropogenic (legacy)
mercury to global atmospheric deposition and
surface ocean
GEOS-Chem based global biogeochemical model of
mercury cycling
Mercury pollution is mainly a legacy problem that
will take centuries to fix all we can do in
short term is prevent it from getting worse
Helen Amos, Harvard
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